Cristobalite-free mullite grain having reduced reactivity to molten aluminum and method of producing the same

摘要

A method of making a cristobalite-free, mullite grain capable of withstanding reaction with molten aluminum, comprising the steps of: producing a clay slurry comprised of water and kaolin clay of a specific particle size; mixing a water insoluble barium or strontium containing compound into the clay slurry in an amount wherein the barium or strontium containing compound content of the slurry is equal to about 8% by weight of the kaolin clay in the slurry; removing sufficient water from the slurry to form a material having an pelletizable consistency; forming the material into pellets; heating the pellets by continuously moving them through a furnace having a zone, wherein the material is exposed to temperatures of at least 2,650° F. (1,455° C.) for at least 30 minutes.